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  • Level: GCSE
  • Subject: Science
  • Essay length: 3299 words

Investigation to find out how light intensity effects the rate of photosynthesis

Extracts from this essay...


Investigation to find out how light intensity effects the rate of photosynthesis Contents * Introduction * Aim * Hypothesis * Variables * Precaution * Fair Testing * Apparatus * Method * Diagram for Method * Results * Analysis of Results and Graphs * Conclusion * Evaluation * Errors, limitations and Improvements Introduction Flowering plants, like all living organisms, need a supply of food. They need it as a source of energy in respiration and they need it as raw material for growth and repair. Animals and most micro- organisms get their food in an organic form: they eat products from other organisms (such as fruit and eggs) or, nowadays, the organic substances made in laboratories and factories. Animals and the microorganisms that do this are called consumers. Due to the flowering plants can make their own organic food from simple inorganic substances and an outside source of energy, they are called producers. Once the producers have made their food they use it in the same way as the consumers do as a source of energy and as raw material for growth and repair Photosynthesis The simple inorganic substances from which flowering plants make their food are carbon dioxide (CO2) and water (H2O). These contain no energy that a flowering plant can use an outside source of energy is needed to combine them into a compound that the plant can use as food. The source of energy is sunlight; the food compound that is made up the simple sugar, glucose (C6H12O6), and the waste product that is left photosynthesis, is shown in an equation as: Carbon dioxide + Water Glucose + Oxygen 6CO2 + 6H2O C6H12O6 + 6O2 Light energy is trapped by photosynthesis and converted into chemical energy in compound glucose. Carbon Dioxide Carbon dioxide is a gas which is present in air only in small amounts about 0.04% of air is carbon dioxide.


* The leaves chosen for the practical must not be variegated or yellow. They must be green. Fair Testing By applying fair testing to a practical, a candidate can be fair in obtaining his or her results. The fair testing I am going to apply to my practical is: - * I will set up the apparatus exactly as shown in my method. * In the effect of light intensity on the rate of photosynthesis experiment, I will use a ruler to measure the distance of the lamp from the jar. * I will count the number of bubbles produced by marking dots on the paper as the bubbles are produced. Then I will count them to write how many bubbles are produced. * I will repeat my experiment twice to improve their validity and reliability. Apparatus 1. Pondweed 2. A beaker of water 3. 10cm3 of sodium hydrocarbonate 4. Funnel 5. Bench Lamp 6. Stop Watch Method 1. Fill a beaker with tap water and add 5cm3 saturated sodium hydrocarbonate solution. 2. Select a pondweed shoot about 2-4cm long 3. Set up apparatus as shown in diagram 4. Place a bench lamp about 8cm away from the beaker, switch on and start the timer 5. Record the number of bubbles produced in ten minutes. 6. Repeat step 1-5, moving the bench lamp to 20cm away from the beaker. Diagram for Method Results The effect of light intensity on the rate of photosynthesis. Lamp at 8cm away from the beaker Time (minutes) Number of oxygen bubbles 1 34 2 56 3 78 4 93 5 108 6 139 7 145 8 158 9 189 10 196 Lamp at 20cm away from the beaker Time (minutes) Number of oxygen bubbles 1 12 2 19 3 33 4 58 5 65 6 74 7 91 8 95 9 99 10 106 Graph for test 1 and 2 Graph for the rate of photosynthesis Analysis of Results and Graphs To work out the gradient I shall use the formula of dy/dx.


Using translucent color filters in front the lamps could vary this. Since light wavelength has already been identified as a variable of photosynthesis, it would be interesting to actually test it. The only problem of this experiment is that there is no way to define or "measure" the color of light. Wavelength would be a solution but this cannot be measured with available equipment. We only have a general idea of how to class colors. Because of this, the colored light experiment should not be taken as seriously as light intensity or carbon dioxide. Errors, Limitations and Improvements Like all experiments there is always room for improvement and this one is no exception. My main limitation was time. If there had been enough time I could have carried out the same experiments but in various different ways, another problem that occurred with my experiment was that the temperature had been fluctuating whilst the lamp was at 8cm from the beaker. I could have done the experiment more than once but this would have been a waste of time as I felt my present results were good enough. I could have used a couple of different types of pondweed to see if this made a difference to the results. If I was to do this experiment again then this is the method that I would use to improve it. * Collect a beaker of 100ml. Fill up to 100ml * Collect a fresh piece of Elodea (Canadian pondweed) about 5cm3 long * Attach the pondweed to two paper clips, so that it is weighed down. Then place the Elodea into the water * Take the funnel and place it over the Elodea upside down * Measure 10cm intervals up to 1m away from the lamp * Start stopwatch when the light is turned on * Count how many bubbles are produced in 2 minutes * And repeat the same experiment 3 times. Hopefully using this method will make a better experiment and produce better primary results, so that secondary data doesn't have to be used. Apart from some problems the experiment went quite well.

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Here's what a teacher thought of this essay

4 star(s)

This is a very well written practical. There are a few errors but they are minor. It is well laid out with a good example of how to write a conclusion.

The writer could improve in some areas such as variables and scientific terminology.


Marked by teacher Sam Morran 15/05/2013

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